1. Field of the Invention
The present invention relates to a touch panel, and in particular relates to a photo sensitive touch panel.
2. Description of the Related Art
Conventional photo sensitive touch panels comprise a sensor thin film transistor (sensor TFT), a readout thin film transistor (readout TFT), and a capacitor for photo sensing function. After the touch panel is illuminated, an amorphous silicon semiconductor layer of the sensor TFT produces a leakage current, a current value of the sensor TFT is read out through the readout TFT and then a voltage value is obtained. The voltage value can represent the strength of light illuminating to the touch panel. Photo sensitive touch panels can be induced by finger pressure or a light pen. The leakage current of the sensor TFT is reduced when a finger pressure thereupon and the leakage current of the sensor TFT is increased when using a light pen. Both of the leakage currents can be distinguished from a read out voltage value in the touch panel without the finger pressure or the light pen.
FIG. 1 shows an illustrative plane view of a sub-pixel of a conventional photo sensitive touch panel. The touch panel has a plurality of sub-pixels 11. Each sub-pixel 11 is defined by two adjacent data lines 10 and two adjacent scan lines 12. Each sub-pixel 11 has one photo sensitive area 16 and one display area 18, and a photo sensor (not shown) is disposed at the photo sensitive area 16. For conventional photo sensitive touch panels, when using a light pen with a light source of three individual colors of red, green, and blue (RGB), each photo sensor thereof needs to be disposed under one of three kinds of RGB color resists for sensing the three light source colors individually. Each of the RGB photo sensors are usually disposed at the sub-pixels with respective RGB color filter films. Therefore, at the single sub-pixel 11 of the conventional photo sensitive touch panels, the color filter films over the photo sensitive area 16 and the display area 18 have the same color. Additionally, pixel electrodes over the photo sensitive area 16 and the display area 18 share the same pixel electrode at the single sub-pixel 11, and the pixel electrodes over the photo sensitive area 16 and the display area 18 are not separated. Thus, the color of light sensed by the photo sensor at the photo sensitive area is the same as the color of the light passing through the display area 18.
Moreover, each photo sensor at each photo sensitive area 16 needs to be connected with a signal readout line 14 for reading signals. Additionally, each sub-pixel has one photo sensor disposed therein, such that each column of the sub-pixels has one signal readout line 14 to connect all photo sensors at one column of the sub-pixels. Therefore, the conventional photo sensitive touch panels have a plurality of signal readout lines 14, which reduces aperture ratio thereof. Additionally, the signal readout line 14 is adjacent to the data line 10, such that the signal readout line 14 may easily interfere with the data line 10, which causes readout errors.
Therefore, a photo sensitive touch panel which can overcome the above mentioned problems, having a higher aperture ratio and reducing readout errors is desired.